A Bose-Einstein condensate was produced in a vapor of rubidium-87 atoms that was confined by magnetic fields and evaporatively cooled. The condensate fraction first appeared near a temperature of 170 nanokelvin and a number density of 2.5 x 10 12 per cubic centimeter and could be preserved for more than 15 seconds. Three primary signatures of Bose-Einstein condensation were seen. (i) On top of a broad thermal velocity distribution, a narrow peak appeared that was centered at zero velocity. (ii) The fraction of the atoms that were in this low-velocity peak increased abruptly as the sample temperature was lowered. (iii) The peak exhibited a nonthermal, anisotropic velocity distribution expected of the minimum-energy quantum state of the magnetic trap in contrast to the isotropic, thermal velocity distribution observed in the broad uncondensed fraction.

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Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor

Single trapped ions represent elementary quantum systems that are well isolated from the environment. They can be brought nearly to rest by laser cooling, and both their internal electronic states and external motion can be coupled to and manipulated by light fields. This makes them ideally suited for quantum-optical and quantum-dynamical studies under well-controlled conditions. Theoretical and experimental work on these topics is reviewed in the paper, with a focus on ions trapped in radio-frequency (Paul) traps.

/pdf/quantum-dynamics-of-single-trapped-ions-5b12pz9r16.pdf

Quantum dynamics of single trapped ions

https://link.aps.org/pdf/10.1103/RevModPhys.70.721

Nobel Lecture: Laser cooling and trapping of neutral atoms

The development of wave optics for light brought many new insights into our understanding of physics, driven by fundamental experiments like the ones by Young, Fizeau, Michelson-Morley and others. Quantum mechanics, and especially the de Broglie’s postulate relating the momentum p of a particle to the wave vector k of an matter wave: k = 2 λ = p/ℏ, suggested that wave optical experiments should be also possible with massive particles (see table 1), and over the last 40 years electron and neutron interferometers have demonstrated many fundamental aspects of quantum mechanics [1].

/pdf/optics-and-interferometry-with-atoms-and-molecules-1vnuwajb51.pdf

Optics and interferometry with atoms and molecules

A single charged particle in a Penning trap is a bound system that rivals the hydrogen atom in its simplicity and provides similar opportunities to calculate and measure physical quantities at very high precision. We review the theory of this bound system, beginning with the simple first-order orbits and progressively dealing with small corrections which must be considered owing to the experimental precision that is being achieved. Much of the discussion will also be useful for experiments with more particles in the trap, and several of the mathematical techniques have a wider applicability.

Geonium theory: Physics of a single electron or ion in a Penning trap

The intrinsic noise of the best quartz crystal resonators is significantly less than the noise observed in oscillators employing these resonators Several problem areas common to traditional designs are pointed out and a new approach is suggested for their solution. Two circuits are described which frequency lock a spectrally pure quartz crystal oscillator to an independent quartz crystal resonator. The performance of the composite system is predicted based on the measured performance of its components.

/pdf/a-frequency-lock-system-for-improved-quartz-crystal-3evigjqqbt.pdf

A Frequency-Lock System for Improved Quartz Crystal Oscillator Performance

Recent data on the miniature (30 kg) passive hydrogen masers developed at the National Bureau of Standards (NBS) in cooperation with the Naval Research Laboratory (NRL) indicate a frequency stability of σ2 y (τ) ≤ (1.5 × 10−12τ−1/2)2 + (5 × 10−15)2 1 s < τ < 5 × 105 s. These masers also have extremely low sensitivity to changes in the external magnetic field or temperature. The sensitivity to barometric pressure and or humidity, although very small, does dominate the residuals in one of the miniature masers for times beyond about a week. Frequency drift is so small as to be hidden in the present measurement precision. The fractional reproducibility under all changes, excluding the storage bulb, appears to be better than 5 × 10−13. The concepts behind the physics and the electronics that made these advances possible as well as present limitations are explained in some detail.

Characteristics and performance of miniature NBS passive hydrogen masers

During the past two decades very important advances have been accomplished in reducing the phase modulation (PM) noise in state-of-the-art bulk wave quartz crystal oscillator. Various limitations have been significantly reduced, especially those related to dynamic temperature fluctuations, temperature gradients, 1/f noise in the electronic and amplitude frequency effects. Amplitude frequency effects have been studied in the past because they are so large in AT-cut resonators. The introduction of the SC-cut significantly reduced the sensitivity to amplitude fluctuations as well as the sensitivity to temperature fluctuations. The amplitude frequency effect in modern SC-cut resonators at 5 or 10 MHz is, however, far from negligible and its importance relative to temperature effects and 1/f amplifier noise must now be reexamined to chart the path to further advances in short-term stability. In this paper we show comparisons of the amplitude frequency effect in traditional 5 MHz AT-cut resonators to our results obtained with 5 MHz BVA AT-cut, 5 MHz BVA SC-cut, 10 MHz BVA AT-cut and several designs of 10 MHz BVA SC-cut resonators. We also compare these measurements with those obtained from 100 MHz resonators. A simple model in which an additional noise source arising from the amplitude frequency effect is introduced in the input of the resonator excited at a given power. This permits us to estimate the contribution of the amplitude frequency effect to /spl sigma//sub y/(/spl tau/).

http://ieeexplore.ieee.org/iel3/4090/12100/00560263.pdf

Phase noise limitation due to amplitude frequency effects in state-of-the-art quartz oscillators

We describe the design of a synthesized local oscillator for a rubidium [Rb] passive frequency standard pumped by radiation from a diode laser. The design goals for this new oscillator are: 1) To operate at room temperature,

Ultra-high stability synthesizer for diode laser pumped rubidium

This paper investigates the phase modulation (PM) noise generated by intrinsic reactance fluctuations in signal carrying components. We report the fractional fluctuation in the reactance of commonly available capacitors, inductors and varactors. Fractional fluctuations were inferred by measuring the phase shift of the carrier signal across the components and the resulting PM noise due to intrinsic fluctuations. In addition, various methods to reduce the effect of intrinsic noise in low noise circuit applications are discussed.

Fred L. Walls

Papers

A Frequency-Lock System for Improved Quartz Crystal Oscillator Performance

Characteristics and performance of miniature NBS passive hydrogen masers

Phase noise limitation due to amplitude frequency effects in state-of-the-art quartz oscillators

Ultra-high stability synthesizer for diode laser pumped rubidium

PM noise generated by noisy components